Webster's Revised Unabridged Dictionary · 1913

Affidavit

Affidavit ({not transcribed}) , noun

[Late Latin affidavit he has made oath, perfect tense of affidare. See Affiance, Affy.]

(Law) A sworn statement in writing; a declaration in writing, signed and made upon oath before an authorized magistrate. — Bouvier

It is always made ex parte, and without cross-examination, and in this differs from a deposition. It is also applied to written statements made on affirmation.